In the field of radio communication, it is previously known to use large array antenna systems. In this regard, the term “array antenna”, or, equivalently, “antenna array” refers to a geometrical arrangement of a number of antenna elements. The antenna elements are configured as a single antenna unit to achieve a desired antenna gain and directional characteristics, i.e. a particular radiation pattern. A variation of this radiation pattern is often referred to as beam-forming.
Antenna arrays find applications, e.g., in multiple-input multiple-output (MIMO) communication systems. In this context, very large antenna arrays are often referred to as “massive MIMO arrays”. Massive MIMO arrays may use several hundreds of antenna elements arranged in a single antenna unit and are considered to be a key technology component for future communication systems, such as fifth generation, 5G, communication. According to known technology, an up-link MIMO unit may comprise for example a radio base-station receiver, an analog-to-digital converter and automatic gain control units.
Another example of related technology is the so-called ultra-dense network (UDN), which uses the millimeter-wave (mmW) band in order to define a network in which the density is so high that each base station is likely to support a single user, or a very limited number of users. The purpose with such a network is to provide a high capacity, in terms of, e.g. data throughput or data rate, in public places such as airports, shopping malls and similar.
For some or all of the above-mentioned technologies, beam-forming is an important component in order to achieve an intended functionality, such as increased capacity and improved coverage. However, large antenna arrays may then become necessary, having a large number of antenna elements. This creates a need for simple and power-efficient antenna hardware components, in particular in scenarios with high power consumption and high data-rate requirements. Another factor which is also important to consider in terms of power consumption and complexity is the digital-to-analog converters (DAC) and analog-to-digital converters (ADC) which are used in transmitters and receivers, respectively.
In the above-mentioned fields of technology, there is a general requirement to provide communication systems involving array antenna units with low power consumption and low cost. As an example, there is a requirement to use ADCs with a low degree of complexity, with relatively low resolution in terms of bits/sample, and having a low current consumption. An analog-to-digital converter of the single-bit type, i.e. a converter in which only one bit is used for each sample in the converter, fulfills these demands.
However, single-bit converters have limited use, since they can normally only operate in communication systems using low-density modulation of a binary pulse amplitude modulation (PAM) type, or quadrature phase shift keying (QPSK) type, i.e. modulations with signal constellations having at maximum two states in an in-phase (I) dimension and two states in a quadrature (Q) dimension, and cannot be properly used in systems using more complex modulating schemes of higher order, such as, e.g., 16-QAM. Consequently, there exists a contradiction in terms of a need for simple converter solutions (such as the single-bit converter) and the requirements for using complex communication systems with more advanced modulation schemes of higher order.
As a further example, it can be mentioned that a typical previously known massive MIMO receiver structure includes low noise amplifiers, mixers, local oscillator sources, high speed ADCs and automatic gain control (AGC) circuitry. This type of hardware architecture generally supports modulation schemes with much larger density than that of, e.g., QPSK modulation, but at a cost of increased complexity and also often a high power consumption. Such properties of an antenna system are not acceptable in situations with limited output power and/or coverage.
Having the above in mind, there exists a general need to increase the capacity and processing speed of array antenna systems but without increasing the cost, complexity and power consumption of such an array antenna arrangement. In particular, there is a need for using simple, low resolution ADCs within the relevant field of technology.